Spin-crossover cobalt(II) complexes exhibiting temperature- and concentration-dependent optical changes in solution.

This work investigated the spin states of the cobalt(II) complexes [Co()](X) (1·X; = 4'-(4-,'-diphenylaminophenyl)-2,2':6',2''-terpyridine, X = PF, BPh) and [Co()](X) (2·X; = 4'-(4-,'-dimethylaminophenyl)-2,2':6',2''-terpyridine, X = PF, BPh) in the solid state and in solution. In the solid state, and , both containing smaller PF counter anions, showed gradual spin-crossover. In contrast, and remained in the high-spin state over the temperature range of 5-400 K due to a lower degree of molecular cooperativity.

Mononuclear Fe(III) complexes with 2,4-dichloro-6-((quinoline-8-ylimino)methyl)phenolate: synthesis, structure, and magnetic behavior.

Three Fe(III)-based coordination complexes [Fe(dqmp)](NO)·HO (1), [Fe(dqmp)](BF)·2CHCOCH (2), and [Fe(dqmp)](ClO) (3) were synthesized from Fe(NO)·9HO/Fe(ClO)·xHO, NaBF, and 2,4-dichloro-6-((quinoline-8-ylimino)methyl)phenol (Hdqmp) in methanol/acetone and characterized. The structures of complexes 1-3 were determined single-crystal X-ray crystallography at 100 K and room temperature, and their magnetic properties in the solid and solution forms were investigated. All complexes showed meridional structures with two tridentate dqmp ligands coordinated with Fe(III) cations.

Cooperative Spin-State Switching and Vapochromism of Mononuclear Ni(II) Complexes by Pyridine Coordination/Decoordination.

Two mononuclear Ni(II) complexes ( and ) have been found to display color changes upon coordination/decoordination of pyridine, resulting in their structural transformation between square-planar and octahedral geometries as well as a change in their spin state. Compound changes between red () and yellow () upon exposure to or elimination of pyridine, while undergoes a two-step transformation, changing orange ( = 0) ⇄ gray ( = 1) → yellow ( = 1) depending on the reaction time. The first step ( → ) takes less than 45 min, which is significantly faster than the previously reported reaction time of 1 day for a Ni(II) complex/pyridine vapor system.

Thermosalient effect of a naphthalene diimide and tetrachlorocobaltate hybrid and changes of color and magnetic properties by ammonia vapor.

An organic-inorganic hybrid metal halide (OIMH), namely the electron-deficient naphthalene diimide (NDI) and [CoCl] hybrid (1), showed potential as a sensor for ammonia and amines, in addition to magnetic changes upon vapochromism. Crystal 1 exhibited thermosalient behavior such as leaping and movement, at around 130 °C, which could be explained to be associated with the removal of water molecules from the crystal lattice as shown by TGA and DSC. Compound 1 changed from green to black within 5 minutes when exposed to ammonia vapor, which was attributed to the radical formation in the NDI moiety as evidenced by ESR, and this phenomenon was preserved even when other mono- and di-alkylamines were applied.

Spin Crossover Induced by Changing the Identity of the Secondary Metal Ion from Pd to Ni in a Face-Centered Fe M Cubic Cage.

Discrete spin crossover (SCO) heteronuclear cages are a rare class of materials which have potential use in next-generation molecular transport and catalysis. Previous investigations of cubic cage [Fe Pd L ] constructed using semi-rigid metalloligands, found that Fe centers of the cage did not undergo spin transition. In this work, substitution of the secondary metal center at the face of the cage resulted in SCO behavior, evidenced by magnetic susceptibility, Mössbauer spectroscopy and single crystal X-ray diffraction.

Air oxidation-induced single-crystal-to-single-crystal transformation of mixed-valence tetranuclear Fe(II)-Fe(III) complexes.

A mixed valence tetranuclear iron complex [(Hpmide)Fe(NCSe)Fe(pmide)]·5CHOH (1) underwent oxidation and ligand exchange in the solid state (Hpmide = -(2-pyridylmethyl)iminodiethanol). Upon air oxidation, 1 was converted into [(pmide)Fe(NCSe)Fe(pmide)](NCSe)·2HO (2), which was accompanied by deprotonation and ligand exchange through a single crystal-to-single-crystal transformation.